In this laboratory,
Jose R. Carraquero demonstrated that toxicity could be
expressed to salmonids only if the Heterosigma were
cultured under longer light period than 12 hours light:
12 hours dark, and only if cultured in an enriched sea
water medium (HESNW), but not if cultured in O-3, a highly
enriched chemically defined medium that we had used for
most of our studies. When grown with continuous
light and in HESNW medium, Heterosigma grown
with bacteria (an algal-bacteria-consortium, ABC, obtained
from Drs. Albright and Yang of the Department of Biological
Sciences, Simon Frazer University, Burnaby, BC, Canada)
was toxic to salmonids (chinook, Oncorhynchus tschawytscha,
coho, O. kisutch, and rainbow trout, O. mykiss).
Neither supernatant nor the bacteria were themselves toxic.
Axenic cultures of Man-1 became toxic when grown with
bacteria from ABC or when frown with either of two t pes
of non-toxic bacteria. Deaths occurred more rapidly when
cultures were grown and fish exposed at 20 C than at 12
C. The toxic cultures produced superoxide radicals, as
measured by a luminol reaction, a measure of superoxide
radicals. Addition of Vitamin C, eliminated the
luminol reaction, but did not prevent mortality. The addition
of a catalase in addition to Vitamin C did eliminate mortality.
This suggests that hydroxyl radicals may have been responsible
for the mortalities, but the role of superoxide, in the
absence of Vitamin C addition, cannot be eliminated. These
data lend strong support to the hypothesis that free radicals
or Reactive Oxygen Species (ROS) are involved in the mortality,
but cannot exclude the potential of other toxic factors
being present. Salmonids exposed to ABC or Man-1 with
bacteria behaved as if anesthetized. Histological examination
of the gills of exposed fish showed edema and a considerable
degree of epithelial separation from the capillary core
of the second lamellae. This could have caused death by
hypoxia by decreasing oxygen and carbon dioxide exchange.
Exposure of Man-1 Heterosigma grown in HESNW
to 4 hours of light intensity including UV-B did not result
in toxicity to salmonids. The algal cultures were
not exposed to UV during the fish exposures. During the
exposure period, the light intensities were (in W/m(squared))
in the treatment (PAR=8.3, UV-A=2.8, and 0.1) as compared
to the controls (PAR=8.2, UV-A=2.5, and 0.002).
These values are only about 2-3% of full sunlight. Luminol
reactions showed no superoxide radicals.